This invention relates to a microelectromechanical or nanoelectromechanical resonator architecture or structure, and method of designing, operating, controlling and/or using such a resonator; and more particularly, in one aspect, to a microelectromechanical or nanoelectromechanical resonator architecture or structure having one or more enhanced nodal points that facilitate substrate anchoring in order to minimize influence of packaging stress and/or energy loss via substrate anchoring.
Generally, high Q microelectromechanical resonators are regarded as a promising choice for integrated single chip frequency references and filter. In this regard, high Q microelectromechanical resonators tend to provide high frequency outputs that are suitable for many high frequency applications requiring compact and/or demanding space constrained designs. However, when the output frequency of the resonator is “pushed” higher while the resonator is being scaled smaller, packaging stress, energy loss into the substrate through substrate anchors and/or instability or movement of the center of gravity during oscillation tend to adversely impact the frequency stability as well as “Q” of the resonator.
There are several well-known resonator architectures. For example, one group of conventional resonator architectures employs closed-ended or open-ended tuning fork. For example, with reference to FIG. 1, closed-ended or double-clamped tuning fork resonator 10 includes beams or tines 12a and 12b. The beams 12a and 12b are anchored to substrate 14 via anchors 16a and 16b. The fixed electrodes 18a and 18b are employed to induce a force to beams 12a and 12b to cause the beams to oscillate (in-plane).
The characteristics and response of tuning fork resonator 10 are well known. However, such resonator architectures are often susceptible to changes in mechanical frequency of resonator 10 by inducing strain into resonator beams 12a and 12b as a result of packaging stress. In addition, conventional resonator architectures, like that illustrated in FIG. 1, experience or exhibit energy loss, though the anchors, into the substrate.
Certain architectures and techniques have been described to address Q-limiting loss mechanism of energy loss into the substrate through anchors as well as changes in frequency due to certain stresses. For example, the beams may be “suspended” above the ground plane and sense electrode whereby the vibration mode of the beam is out-of-plane. (See, for example, U.S. Pat. No. 6,249,073). While such architectures may alleviate energy loss through the anchors, resonators that include an out-of-plane vibration mode (i.e., transverse mode) tend to exhibit relatively large parasitic capacitance between drive/sense electrodes and the substrate. Such capacitance may lead to a higher noise floor of the output signal (in certain designs).
In addition, such a resonator requires at least one additional mask to fabricate, as compared to the in-plane vibration resonator, in order to define the drive/sense electrode. Notably, conventional resonator architectures implementing the “suspended” beam configuration remains susceptible to a “moving” center of gravity during oscillation which may adversely impact the frequency stability as well as “Q” of the resonator
Other techniques to improve the Q-factor of the resonator have been proposed and include designing the spacing between the vibrating beams so that such beams are closely spaced relative to a wavelength associated with their vibrating frequency. (See, for example, the single-ended or single-clamped resonator of U.S. Pat. No. 6,624,726). The vibrating beams are driven to vibrate one-half of a vibration period out of phase with each other (i.e., to mirror each others motion). While these architectures and techniques to improve the Q of the resonator may suppress acoustic energy leakage, such an architecture remain predisposed to packaging stress, energy loss into the substrate through substrate anchors as well as a “moving” of the center of gravity of the resonator during motion by the vibrating beams of the single-ended or single-clamped resonator.
Thus, there is a need for a resonator architecture, configurations or structure, and method of designing, operating, controlling and/or using such a resonator that overcomes the shortcomings of one, some or all of the conventional microelectromechanical resonator architectures, configurations or structures. In this regard, there is a need for improved microelectromechanical and/or nanoelectromechanical resonators having improved packaging stress characteristics, reduced and/or minimal energy loss into the substrate though substrate anchors, and/or improved or optimal stability of the center of gravity during oscillation. In this way, the stability and/or linearity of the output frequency of the resonator is enhanced and/or the “Q” factor of the resonator is high.